a lot of these super compacts now not only have an optical zoom, but they also "boast" a digital zoom

so is it logical to say that when you have a FF DSLR with a bigger sensor plus more mega pixels and you use say a 50mm lens and then crop it down, that is equivalent to what may be called a "digital zoom" image

what I am after is info on digital zooms versus optical zooms and their comparison

the concept being - i.e. which will have the best IQ - a Nikon D700 with a 50mm, 100mm or 200mm lens cropped down to the same size as a super compact producing an image at the 35mm equivalent of 500mm or whatever - someone needs to do the maths for me, i.e. sensor size, pixels and crop factor

what I am asking is "is a DSLR cropped image a digital zoom image and are their any comparisons anywhere between cropped images from a DSLR versus "optical" zoom images from a super compact ........... if you get my drift ........ is a (cropped) digital zoom image from a DSLR better IQ wise that an optical zoom image from a good compact, (say the XS-1) - and were does the IQ cross over?

am I talking a load of rubbish or can someone enlighten me

another realted thought, to confuse, is - all you will need one day is say, a D800 plus a 100 mm lens - then crop it down and you will have an image better than any 500mm super zoom compact ....... and once you stick a 200mm prime on the end ...... and crop - no need for all these long VR lens - (accepting that most never fill the frame)

I think many cameras res up the image when they apply digital zoom - so the total megapixels remain the same, using interpolation to fill in the missing pixels, with obvious consequences for the image quality.

If you simply crop a 100mm D700 image down to 500mm FOV, you're left with a roughly 855*570pixel image, which isn't enough to fill the screen. You might be able to res it up, but then you lose the sharpness advantage. Now if you use a D800, with its 36mp sensor, you'd still have a 1469*979 pixel image, which is already a much more useful resolution. Ofcourse, with both cameras, you'd be using only the very centre of your lens which is usually the sharpest, and a lot sharper than a superzoom's lens.

So if 100mm is wide enough for you, and the remaining pixels from the strong crop are enough for you, I think you'd end up with better IQ. If the remaining pixels aren't enough for you and you have to res up the image, I think you'd be better off with the superzoom.

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